Jim,
"what about mechanical limit switches on the rotator motor?"
A possibility but that's probably best done when these units are back on the
ground for service. That shouldn’t be for quite a long time.
"Since it's a DC motor, you put a diode in series with each of the two
switches, which are then paralleled."
Maybe I'm just being dense this morning, but I don’t see how a
series/parallel diode combination helps in this case. I just drew-out the
electrical diagram but don't see how the diode would limit current during an
MOV fault while still allowing rotator current during a normal turning
operation.
A bit more info: The prop pitch uses two windings: one for CW and the other
for CCW. A common lead connects to the ends of each and ultimately, this
common lead routes to the controller's MOSFET. The M2 controller uses a P&B
frame relay that directs +48V to either the CW or CCW winding, depending on
the called direction. The relay's NC contacts are on one or the other
windings. I forgot which. But the MOV failure would result in current in
this NC winding since its connected to +48V via the NC relay contact.
Paul, W9AC
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